1997 Blazer needs a fuel pump with sending unit ...

Not sure what to get? There's a few listed -which ones the right one with out having the car in front of me?
Is there really a difference between the 4dr and 2dr pumps?

 

There is a little tag on top of the fuel pump. You need that number, at least that was the deal on my '00.

Get the best one you can afford, GM original or one with a lifetime warrenty.

 

The tanks are different between the 2dr and 4dr. And as Tim already stated, you will want to match up the number on your current pump with that of the replacement, regardless of what you choose to put in.